Latest Situation Updates
This report gives an update on the previously reported stem rust outbreak in southern Ethiopia (see http://rusttracker.cimmyt.org/?p=5473). Thanks to extensive surveillance and sampling, more details are now available regarding the areas affected and also the likely causal race.
Based on surveys and information received, up to 17 woredas (districts) in Oromia and SNNPR regions may have been affected to some degree by the stem rust epidemic (see overview map). Based on Ethiopian Central Statistical Agency (CSA) data from 2001, total wheat area in these woredas is approximately 91,000 ha. Based on field observations it is not unrealistic to assume that the susceptible cultivar Digelu might occupy 20-40% of the areas planted. A very rough, approximate, estimate of the area that may have been affected to some degree by stem rust is therefore 18,000 – 36,000 ha (i.e., approximately 1-2% of the total Ethiopian wheat area). More precise area estimates will hopefully be available in the future. Detailed crop loss assessments for the Bale zone are in progress, but no results are available yet.
Survey and sampling data currently available indicate the first outbreaks occurred in the general area of Agarfa/Gasera / Arsi Robe, most likely in late September 2013, then there appeared to be spread in a south-westerly direction into SNNPR region. Such movements would correspond to the previous predictions for spore dispersal made by the Cambridge University modelling group. The potential source of the initial outbreak is unknown.
Surveys in Arsi Robe/Diksis/Sude on 21st Jan 2014 revealed widespread high incidence (100%) and severity (up to 80%) of stem rust on Digelu. The situation was somewhat better than that observed in Agarfa/Gasera in Nov 2013, in the respect that no fields with 100% crop loss were observed. However, disease pressure continued to be very high in this area. The cultivar Danda’a was observed to have much lower severity of stem rust compared to Digelu.
The stem rust race implicated in the epidemic has been tentatively identified as race TKTT-, using North American nomenclature. This race is NOT part of the Ug99 race group. At present there is some uncertainty around the effectiveness of gene Sr38 in respect to this race, hence the last letter of the race code is currently blank. Further tests are on-going to resolve this issue. The race has confirmed virulence on the following resistance genes: Sr5, 21, 9e, 7b, 6, 8a, 9g, 36, 9b, 30, 17, 9a, 9d, 10, Tmp, McN. It is confirmed avirulent on: Sr11, 24, 31. The virulence on SrTmp is believed to be the key factor for the susceptibility of Digelu. Further analysis is on-going to definitively confirm this as the causal race.
This race, prior to Sep/Oct 2013, had not been detected in Ethiopia. The assumption therefore is that this is either a foreign incursion (most likely by wind) or a mutation in-country. The same (or similar) race is already known from other countries: Turkey (in 2007, 2008, 2011, 2012); Lebanon (in 2012); Egypt (in 2013); Germany (in 2013). Studies are underway to determine how related the races in different countries might be through DNA fingerprinting.
No reports of race TKTT- have yet been confirmed from any the countries neighbouring Ethiopia. However, survey and sampling activities are taking place in several countries to monitor potential spore movements.
(NB: This report was updated with new information on 10th March 2014)
Following the recent surveys and sampling in Rwanda by the Rwanda Agriculture Board (RAB), wheat program and CIMMYT-Ethiopia during the period 27th Jan – 1st Feb 2014; two known Ug99 races have now been identified. Molecular diagnostic assays carried out by Dr Les Szabo at the USDA-ARS Cereals Disease Lab, Minnesota confirmed the presence of races TTKSK (original Ug99) and TTTSK (Sr36 variant of Ug99) in Rwanda. Race TTKSK was dominant, being identified in 13 samples from four dispersed locations (Kinigi RS, Rusarabuye, Rwerere RS and Sigira RS – see map). Two distinct genotypes of race TTKSK (AF-001aa and AF-001ad) were identified in the samples analysed. Race TTTSK (genotype AF-001cc) was detected in 2 samples collected at Sigira RS in the southern province. The results obtained from Rwanda make it the 12th country in which the Ug99 race group has been identified. The races and genotypes detected match those previously known from Uganda and Kenya, so are not unexpected. No evidence was found to indicate the presence of the race implicated in the recent stem rust epidemic in Ethiopia.
During the period 27th Jan – 1st Feb 2014 scientists from the Rwanda Agriculture Board (RAB), wheat program and CIMMYT-Ethiopia conducted wheat rust surveys and sampling in wheat growing areas of the Northern and Southern provinces. These surveys led by Innocent Habarurema (RAB) represent one of the first attempts to understand the status and population composition of wheat rusts in Rwanda. A total of 7 unique, dispersed locations (4 research stations and 3 farmer field sites – see Rwanda Survey Mapper) were included in the survey. Yellow rust and stem rust predominated; with yellow rust being recorded at all locations surveyed and stem rust recorded at all but one location. Leaf rust was not common, only recorded at one location. Disease pressure was higher on research stations vs farmer fields, especially for stem rust. Given the importance of the region for emerging new races of both stem and yellow rust, a key priority of the surveys was sampling to determine which races of rust are currently present in Rwanda. Another important reason for surveys was the spore dispersal modelling work, undertaken by Cambridge University, UK, from the recent stem rust outbreak in Ethiopia.
Model predictions of spore dispersal from the Ethiopia stem rust outbreak indicate the potential for spore movement in a south-westerly direction, with a very low probability that spores may travel as far as Rwanda. Although Rwanda is at very low risk of any spore dispersal from Ethiopia, monitoring of the rust situation in the country was considered a priority in light of this recent outbreak. A total of 14 stem rust samples (live samples plus corresponding DNA samples) and 13 yellow rust samples were collected. The samples aimed to be representative of different geographical areas and different cultivars grown. Samples are currently undergoing analysis at the Cereals Disease Lab, Minnesota, USA and the Global Rust Reference Centre, Denmark and results will be forthcoming.